Microdosimetric approach to the modelling of oxygen effect for the inclusion in treatment planning for charged particle therapyMicrodosimetric approach to the modelling of oxygen effect for the inclusion in treatment planning for charged particle therapy

Biological advantages of heavy ions are characterised by an increased relative biological effectiveness (RBE) and decreased oxygen enhancement ratio (OER). This latter implies a better efficiency for treatment of hypoxic tumours, which are typically radio-resistant. While RBE is taken into account during treatment planning, OER is not yet.Different approaches to consider OER as a dose modification factor have been proposed, as a function of the oxygen concentration and LET of the particles but the different effect of ions at the same LET is not accounted for. At NIRS, the microdosimetric kinetic model (MKM) is used to compute the RBE and the biological dose. Our study aims at including the oxygen effect in the MKM.Results indicate that through the adaptation of parameters such as the quantity of damages and the size of the domains included in the nuclei, it is possible to reproduce cell survival data in hypoxic conditions. Data of two cell lines, V79 and HSG have been used. The behaviour in terms of OER as a function of LET can be reproduced, with a dependence on the ion species. Errors on the prediction of survival for hypoxic data are of the same order of magnitude than of oxic data. Future work will aim at verifying the validity of such modifications at several oxygen pressures, and for chronic hypoxia conditions. The biological optimisation of treatment planning will allow for a better quantification of the advantages of charged particles, as well as the potential to improve treatments using dose or LET boosts.The 55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG55)